Welding is a fabrication or process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work-piece and/or adding a filler material to form a pool of molten material, a.k.a., the weld pool. After the weld pool cools, a high strength joint is produced.
The quality, and therefore the strength of the welded joint is closely related to surface conditions of the work-piece, such as contamination and oxide formation on the surface of the substrates. Furthermore, depending on the type and quality of the materials sought to be joined, the same welding process may expend/consume vastly different amounts of energy to generate a robust weld.
A welding process that expends more energy may require larger, heavier, more powerful, and thus more expensive welding equipment. Such increased consumption of welding energy tends to reduce the overall efficiency of the welding operation, and, coupled with the higher cost and footprint of the welding equipment, tends to increase the effective cost of the finished assembly.